1. Field of the Invention
The present invention relates to a method of vapor depositing a film. More particularly, the present invention relates to a method of vapor depositing a film in which the film is not thermally damaged or broken by a heat for melting a vapor deposition material in vapor deposition preparation steps, and a loss of the film can be decreased as low as possible in the preparation steps.
2. Description of the Related Art
Vapor deposition techniques are applied to polymer films used in a wide variety of usage such as magnetic tapes for backing up data and recording images, wrapping films, and electrode films.
In the magnetic recording usage, a medium is required to have high density, or a tape should be thin, accompanied by a development of a mass storage but small-sized magnetic recording system. A vapor deposition type magnetic recording medium has advantages in the high density recording as compared with a coating type medium. For example, a magnetic layer of the vapor deposition type medium includes no binder, and therefore is filled to higher degree, whereby saturation magnetization can be increased. Also, the vapor deposition type medium can have thin films, whereby recording demagnetization can be prevented even if a recording is performed at a shorter wavelength.
As the conventional vapor deposition medium, a polymer support film such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) is used as a support material on which a film is vapor-deposited, and a ferromagnetic metal such as Co and a Co—Ni alloy forms a magnetic layer on the material to be vapor-deposited. The vapor deposition technique generally utilizes continuous vapor deposition using an electron beam for vaporizing the metal, while the polymer film is moved such that it is held by a cooling drum.
In this case, it is required to preheat (melt) the material to be vapor-deposited and a crucible, in order to vaporize the material to be vapor-deposited continuously and stably upon the vapor deposition. In the preheating, the polymer film can be thermally damaged by radiant heat accompanied by heating a vapor deposition source, which results in a broken film. To overcome the problem, a shielding plate that can be opened and closed is disposed between the material to be vapor-deposited and the polymer film, thereby shielding the heat. Or, the polymer film is held by the cooling drum. However, these measures are not sufficient. Accordingly, while the film is moved at low speed, melting is conducted.
Even if the vapor deposition is performed using the above-mentioned way, a moving part leads a loss upon melting even at low speed. The melting significantly limits an efficient use of the film.
Recent magnetic recording medium is required to have mass storage. A total thickness of the tape is required to be thin in order to lengthen a winding length per a tape. The material having high Young's modulus is getting used as the polymer film since such material can provide strength when the tape becomes thin.
Representative examples of the film having high Young's modulus include aromatic polyamide (aramide) films. When such aramide film is used, heat resistance becomes higher than that of PET or PEN. However, the film is extremely electrified by secondary electrons or recoil electrons produced by irradiating the electron beam to the vapor deposition source. When the film is molten while the film is moved at low speed, the electrified film is unfavorably adhered to the cooling drum, whereby the film is easily broken upon peeling, and the movement becomes unstable.